Fluid-pressure actuated press-tool equipment

ABSTRACT

To avoid damage to press-tool equipment, to the workpiece and/or to a body obstructing the path of the tool during its approach to the beginning of the working stroke, a hydraulic actuating piston is bypassed by a passage including a port which is blanked-off by the piston entering a blanking cover due to the piston movement when the tool commences its working stroke proper.

ilnited States Patent [191 Hilton 1 May 29, 973

{ FLUID-PRESSURE ACTUATED PRESS- [56] References Cited TOOL EQUIPMENT UNITED STATES PATENTS Inventor: J n sli H ng 1,745,549 2 1930 Marghitan ..72 4s3 Hampshire, England 2,784,704 3/1957 Meats ..9l/401 v 3,042,244 7/1962 Van Hecke.. .....72/391 3] Ass1gnee= Plessey Handel d Investments 3,362,211 1/1968 Chirco ..72/391 A.G., Zug, Switzerland 3,534,580 10/1970 Chirco ..72/391 [22] Filed: 1971. Primary ExaminerCharles W. Lanham Assistant ExaminerGene P. Crosby [21] Appl- 196,052 Attorney-Samuel Scrivener, Jr., N. Douglas Parker,

David S. Scrivener et a]. Foreign Application Priority Data [57] ABSTRACT Nov. 10, 1970 Great Britain ..53,314/ To Avoid damage to presmool equipment, to the i v workpiece and/or to a body obstructing the path of [52] US. Cl. ..72/453, 91/399, /53 the tool during its approach to the beginning of the [51] Int. Cl. ..B21j 9/12 working stroke, a hydraulic actuating piston is 58 Field of Search "72/453, 391, 114; yp y a passage including a p which is blanked-off by the piston entering a blanking cover due to the piston movement when the tool commences its working stroke proper.

4 Claims, 1 Drawing Figure 1 FLUID-PRESSURE ACTUATED PRESS-TOOL EQUIPMENT This invention relates to press-tool equipment which is operated by fluid pressure acting on a piston element, and in which an operating portion of the stroke, in which a relatively high actuation pressure is required,

is preceded by an approach stroke in which normally very little resistance is encountered and in which accordingly the pressure should be very much lower than during the operating stroke. The provision of such approach stroke is necessary more particularly in presstool equipment in which separation of the tools by liable to cause damage to the machine, the workpiece,

and/or the obstructing body itself,-and the present invention has for an object to provide improved press equipment which reduces this risk of damage.

According to the inventionthe pressi equipment is provided with a relief passage, which-bypassesthe piston element during the approach stroke and includes arelief valve preloaded so as to prevent flow through the passage from the high-pressure side to the low-pressure side of the piston element'unless apredetermiiiedmaxi mum approach pressure'is'exceeded, cut-off means operable by the displacementof the piston elementbeing further provided which prevent, from a point determining the transition of the piston elementfrom the ap- 'proach stroke to the operating stroke, such flow through the passage from thehigh-pressuresideto the low-pressure side of the piston element. It will be generally preferred to make these cut-off means adjustable so that the equipment can be adapted to varying starting points of the operating stroke.

With this arrangement, if during the approach stroke an obstruction is encountered which cannot be overcome by the action of the preset maximum approach stroke pressure, any actuating fluid delivered to the high-pressure side of the piston element will pass to the ow-pressure side through th passage com g the relief valve, thus preventingthe piston element' from exerting a force higher than that preset for the approach stroke. Conveniently the relief passage'is'ar ranged in the piston element and terminates in a port at the circumference of the latter, for'example at the circumference of the piston rod, which co-operates with a blanking member, which may beintegral with the cylinder end piece, so as to be blanked ofi as soon as the starting point of the operating stroke or working stroke of the equipment is reached.

In order that the invention may be more readily understood, one embodiment as applied to a riveting tool is illustrated in the accompanying drawing, which is a' somewhat diagrammatic axial section of the embodiment, and while a riveting tool has been shown for ease of illustration, it will be readily appreciated that the invention is applicable to a great variety of other presstool equipment, more particularly to crimping tools for electrical connections.

Referring now to the drawing, a hydraulic cylinder 1 contains, in working engagement with it, a piston 2 which is formed integral with a ram-like piston rod member 12 and divides the interior of the cylinder into a high-pressure zone 3 connected to a high-pressure inlet passage 3a, and a low-pressure zone 4. The latter communicates with a low-pressure reservoir or the like by a low-pressure passage 4a penetrating the cylinder wall. The cylinder is closed at its high-pressure end by an integral end portion 9 and at its low-pressure end by a cylinder-end member 7.

The piston element, which consists of the piston 2 proper and the piston-rod member 12, is formed with an axial bore 5 which forms part of a relief passage communicating with the low-pressure part4 of the cylinder by a cross bore 8 in the piston rod 12, and with the high-pressure end 3 of the cylinder via a ball-type relief valve 6. This valve is loaded by a spring 13 accommodated in the bore 5 to keep the valve closed unless the pressure in the high-pressure end 3 of the cylinder exceeds that in the bore 5 by a predetermined or preset value which is well below the working pressure for which the press-tool is designed. Preferably this valveis only just suflicient to overcome any resistance which is likely to be encountered in a normal'approach stroke. This arrangement is is shown as forming part of a riveting press. The end of the stem 12' is formed as a rivet-head forming die having a recess 14 adapted to shape a rivet headwh'enengaging'the end of the stern of a countersunk-type rivet 15 which extends through two metal layers 17 and 18and is supported against an anvilplate 19 connected'to the cylinder body 1 as indicated'by chain-dotted lines 20. The press-tool equipment-is illustrated in its position when'fully open to facilitate the introduction of the assembly to be riveted, and it will be readily appreciated that the press-tool stem 12 willhave to travel a distance indicated as a by way of an approach stroke before the bottom of the rivet-forming recess 14 makes contact with the stem of the rivet 15 to begin the high-pressure operating stroke constituting the working stroke proper. It will further be seen that during the approach stroke any obstruction which offers to the movement of the piston 2 a resistance force exceeding a predetermined value, will cause the'relief valve 6 to open and thus allow any additional operating fluid introduced by the passage 3a into the high-pressure zone 3, to reach the low-pressure outlet passage 4a and escape to the low-pressure reservoir without moving the piston 2. In the illustrated embodiment the cylinder-end member 7 also constitutes a blankingcover for the cross-bore 8. It is adjustable to some extent longitudinally of the cylinder by a screwthread connection 10, and it has an axial bore 11 for sliding co-operation with the piston-rod member 12. The distance of the port formed in the piston-rod member 12 by the cross-bore 8 from the inner blanking surface of the cylinder-end member 7 is so chosen that, when the piston 2 has reached the end of its approach stroke, the port constituted by the outer end of the passage 8 is blanked-off by the wall of bore 11 in the cylinder-end member 7, thus preventing any further flow of working fluid from the high-pressure zone 3 to the lowpressure zone 4 at the opposite side of the piston 2 so that, once this starting point of the working stroke has been reached, full operating pressure of the working fluid is available for displacement of the press-tool stem 12, or in other words for the execution of the pressing operation proper.

What I claim is:

1. Press-tool equipment which includes in combination; a piston element having a high-pressure side and a low-pressure side for operation by a fluid-pressure difference between said sides to carry out a working stroke preceded by an approach stroke, the equipment being provided with a relief passage which bypasses the piston element during the approach stroke, and which includes a relief valve preloaded so as to prevent flow through the passage from the high-pressure side to the low-pressure side of the piston element unless a predetermined maximum approach pressure is exceeded, and cut-off means, operated by the displacement of the piston element beyond a point determining the transition of the piston element from the approach stroke to the operating stroke, to prevent such flow through the passage.

2. Press-tool equipment as claimed in claim 1, wherein the said shut-off means are so constructed as to be adjustable for adapting the equipment to varying starting points of the operating stroke.

3. Press-tool equipment as claimed in claim 1, which includes a cylinder cooperating with the piston element and divided by it into said high-pressure side and said low-pressure side; and a piston rod fixedly connected to the piston element and having a port on its surface at the low-pressure side of the piston element said passage extending longitudinally in the piston rod to connect said port with the high-pressure side of the cylinder, and a cylinder-end member closing said cylinder at the low-pressure side, said end member having an axial bore slidingly co-operating with said surface of the piston rod to blank said port at the end of the approach stroke.

4. Press-tool equipment which includes in combination a piston element having a high-pressure side and a low-pressure side so as to be operable by a fluidpressure difference between said sides to carry out a working stroke preceded by an approach stroke, and means for limiting such pressure difference during the approach stroke. 

1. Press-tool equipment which includes in combination; a piston element having a high-pressure side and a low-pressure side for operation by a fluid-pressure difference between said sides to carry out a working stroke preceded by an approach stroke, the equipment being provided with a relief passage which by-passes the piston element during the approach stroke, and which includes a relief valve preloaded so as to prevent flow through the passage from the high-pressure side to the low-pressure side of the piston element unless a predetermined maximum approach pressure is exceeded, and cut-off means, operated by the displacement of the piston element beyond a point determining the transition of the piston element from the approach stroke to the operating stroke, to prevent such flow through the passage.
 2. Press-tool equipment as claimed in claim 1, wherein the said shut-off means are so constructed as to be adjustable for adapting the equipment to varying starting points of the operating stroke.
 3. Press-tool equipment as claimed in claim 1, which includes a cylinder co-operating with the piston element and divided by it into said high-pressure side and said low-pressure side, and a piston rod fixedly connected to the piston element and having a port on its surface at the low-pressure side of the piston element said passage extending longitudinally in the piston rod to connect said port with the high-pressure side of the cylinder, and a cylinder-end member closing said cylinder at the low-pressure side, said end member having an axial bore slidingly co-operating with said surface of the piston rod to blank said port at the end of the approach stroke.
 4. Press-tool equipment which includes in combination a piston element having a high-pressure side and a low-pressure side so as to be operable by a fluid-pressure difference between said sides to carry out a working stroke preceded by an approach stroke, and means for limiting such pressure difference during the approach stroke. 